Heat broiler to high. Mix mayonnaise, red pepper flakes, 1 tsp. garlic, 1 tsp. orange zest, and 1/2 tsp. salt in a small bowl.
Arrange cod fillets on a rimmed baking sheet. Spread mayonnaise mixture over each fillet.
Toss fennel, broccolini, orange, beans, oil, rosemary, and remaining garlic, 1 tsp. orange zest, and 1/2 tsp. salt in a large bowl. Arrange around fish on baking sheet, placing orange slices on top of beans and vegetables.
Place baking sheet under broiler and broil until fish is golden-brown on top, about 5 minutes. Remove from oven, top each fillet with almonds, then continue to broil until almonds are toasted and crisp and fish is completely cooked through, about 1 minute more.