Halibut and Vegetable Stew
1 lb. firm white skinless fish fillets (such as mahi-mahi, cod, or halibut), cut into 2" pieces
Kosher salt, freshly ground pepper
1 Tbsp. fresh lemon juice
1 Tbsp. red wine vinegar
1/2 tsp. Dijon mustard
3 Tbsp. extra-virgin olive oil, divided
1 cup dry or instant polenta (coarse cornmeal)
1 garlic clove, smashed
1 medium yellow bell pepper, seeds and ribs removed, cut into 2" pieces
1 medium zucchini, cut into 2" pieces
1 pint cherry or grape tomatoes, halved
1 Tbsp. slivered fresh basil (or 1 tsp. dried), plus whole leaves for serving
1 tsp. chopped fresh oregano (or 1/2 tsp. dried), plus whole leaves for serving
Season fish with salt and pepper. Whisk lemon juice, vinegar, mustard, and 2 Tbsp. oil in a medium bowl. Add fish, toss to coat, and chill until ready to use.
Cook polenta according to package directions.
Meanwhile, heat remaining 1 Tbsp. oil in a large skillet over medium-high. Cook garlic, stirring occasionally, until beginning to brown, about 2 minutes. Transfer garlic to a plate.
Cook bell pepper in same skillet, stirring frequently, until beginning to brown and soften, about 3 minutes. Add zucchini, cover, and cook 3 minutes.
Reduce heat to medium-low. Add tomatoes, garlic, fish and dressing, 1 Tbsp. slivered basil, and 1 tsp. chopped oregano; season with salt and pepper. Cover and simmer just until fish is cooked through, about 5 minutes. Discard garlic, if desired.
Divide polenta among bowls. Arrange fish mixture over. Garnish with basil and oregano.