Skip to Content

Oven-Roasted Halibut with Caramelized Red Onions

Sharing is caring!

Oven-Roasted Halibut with Caramelized Red Onions

Oven-Roasted Halibut with Caramelized Red Onions

Jessica Braider
With just the right balance of sweet and savory, this simple fish preparation is sure to please the whole family. If you prefer, you can grill the halibut instead of roasting it.
Cook Time 30 minutes
Total Time 30 minutes
Course Main Dish
Cuisine American
Servings 4 servings


  • 1 Tbsp. extra virgin olive oil
  • 1 large red onion halved and cut into half rings
  • 1 1/2 lbs. halibut fillet, or use cod or mahi mahi
  • 1/8 tsp. salt or to taste
  • 1 Tbsp. Dijon mustard (use wheat/gluten-free if needed)
  • 1 Tbsp. reduced-fat mayonnaise (or use any variety), or use olive oil
  • 4 tsp. balsamic vinegar
  • 1 tsp. honey


  • In a medium skillet, heat the oil over medium-high heat. Add the onions, partially cover the skillet, and cook them until they start to sizzle and brown, 8 - 10 minutes. Remove the lid and reduce the heat to medium. Continue cooking, stirring the onions occasionally, until they start to shrink and are well browned, about 10 more minutes.
  • While the onions are cooking, preheat the oven to 450 degrees (or preheat the grill to medium-high heat). Line a baking sheet (or a fish-grilling tray or the grill) with aluminum foil and spray the foil with nonstick cooking spray.
  • Put the fish on top of the foil, skin side down, and season it with the salt.
  • In a small bowl, whisk together the mustard, mayonnaise, 1 Tbsp. vinegar and the honey.
  • Brush the mixture liberally over the flesh of the fish. Roast the fish in the oven for 10 - 15 minutes (or grill it for 10 - 12 minutes) until a knife slides easily into the thickest part of the fillet and the middle of the fish is white.
  • A few minutes before the fish is fully cooked, add a splash (about 1 tsp.) of balsamic vinegar to the onions and stir them thoroughly. Remove the fish from the oven to a serving plate. Top it with the onions or serve them on the side.

Slow Cooker Directions

  • Cut the fish into pieces that will easily fit into the slow cooker, if needed. Lay each piece of fish on a square of aluminum foil large enough to form a packet around the fish and season the fish with a dash of salt. Whisk the mustard, mayonnaise, 1 Tbsp. vinegar and honey as directed, and brush a roughly equal amount of the mixture over each piece of fish. Form a packet around each piece of fish, and place the packets in the slow cooker, stacking as necessary. Cook on low for 7 - 8 hours or on high for 3 - 4 hours. Caramelize the onions as directed above, and serve over or beside the fish. (Slow cooker cooking times may vary—Get to know your slow cooker and, if necessary, adjust cooking times accordingly.)


Do Ahead or Delegate: Halve and slice the onion, caramelize the onions and refrigerate, prepare and refrigerate the mustard-mayonnaise mixture.
Scramble Flavor Booster: Use grainy Dijon mustard in the marinade and season the fish with freshly ground black pepper before serving.
Tip: When caramelizing onions, resist the urge to stir them too often when they are at the beginning stages of cooking. As they get browner, you can stir them a little more often to keep them from burning.
Nutritional Information Per Serving (% based upon daily values): Calories 260, Total Fat: 10g, 15%; Saturated Fat: 2g, 8%; Cholesterol: 55mg, 18%; Sodium: 350mg, 15%; Total Carbohydrate: 5g, 2%; Dietary Fiber: 0g, 0%; Sugar: 4g; Protein: 37g
Like this recipe? Check out The Scramble's family-friendly meal plans to see just how simple getting dinner on the table can be!
Keyword 30 Minutes (or less) Meals, All, Company/Entertaining, Dairy-Free, Dinner, Fall, Gluten-Free, Grilling, Kid-Friendly, Kosher, Low Carb, Low Fat, Low Sodium, Main Dish, Make-Ahead, Nut-Free, Slow Cooker, Spring, Summer, Winter
Tried this recipe?Let us know how it was!
Recipe Rating

    Your Cart
    Your cart is emptyReturn to Shop