Preheat oven to the broil setting (about 500 degrees). Mince garlic cloves and cut tomatoes into halves then set aside.
Heat olive oil in a large, oven-safe skillet over medium-high heat (about one minute. Add garlic, tomatoes, and crushed red pepper to skillet and cook until tomatoes begin to break down and garlic becomes fragrant (about three minutes).
While tomatoes and garlic cook, season salmon with sea salt, black pepper, and a squeeze of lemon juice.
Push tomatoes to the perimeter of the skillet, leaving space in the center. Add butter to center of pan and allow to melt (about 45 seconds).
Add salmon to pan on top of melted butter and cook until edges start to become opaque (about 3 minutes).
Transfer pan to preheated oven and roast salmon for about eight minutes or until salmon is opaque and cooked through, and tomatoes are blistered. For safe consumption, the internal temperature of the salmon should reach 145 degrees. If you don't have a meat thermometer and are unsure, use a knife to separate one filet in the center. It should flake easily and be opaque.
Serve salmon and tomatoes over a bed of fresh spinach.