Pat the 46 oz halibut fillets dry with paper towels and season both sides with Salt and freshly ground black pepper.

Heat a large skillet with a lid over medium-high heat. Add 2 tablespoons olive oil and heat until shimmering. Add 2 tablespoons unsalted butter and swirl until melted.

Add the halibut fillets, skin-side up or presentation-side down, and sear without moving until the bottom is golden brown, about 3 minutes. Do not overcrowd the pan; sear in batches if necessary. Transfer seared fillets to a plate.

Reduce the heat to medium and add ½ cup chopped red onion to the skillet. Cook, stirring occasionally, until the onion is soft, about 4 minutes.

Add 4 cloves minced garlic and cook, stirring, until fragrant, about 30 seconds.

Stir in 1 teaspoon chopped rosemary and 1 teaspoon chopped thyme, then add ¾ cup halved cherry tomatoes. Cook, stirring occasionally, 1 to 2 minutes to soften the tomatoes.

Pour in ⅔ cup chicken broth and add ½ cup drained and rinsed cannellini beans. Bring the mixture to a gentle simmer.

Add the 5 oz spinach in batches if it won’t fit all at once, stirring each addition until completely wilted before adding more.

Stir in 2 tablespoons lemon juice, ½ cup pitted halved green olives, and the pinch of red pepper flakes. Taste and adjust seasoning with Salt and freshly ground black pepper as needed.

Turn the heat to medium-low. Nestle the seared halibut fillets into the vegetables and sauce, cover the skillet, and cook about 3 minutes (or until the fillets reach an internal temperature of 130–135°F and are cooked through).

Spoon the vegetable-and-bean sauce into shallow bowls, place a halibut fillet in each bowl, spoon more sauce over the top, and serve immediately.