Place a large heavy-bottomed pan over medium high-heat and add the oil. Sprinkle the shrimp with salt and, working in batches, cook until they begin to turn pink on both sides, 3 to 5 minutes. Repeat with the remaining shrimp and set aside.
Add the garlic, carrots, fennel and onions with a large pinch of salt and cook, stirring occasionally until the vegetables soften and begin to caramelize, about 5 minutes.
Stir in the crushed red pepper flakes if using. Add in the white wine and tomatoes and bring to a simmer. Cook, partially covered, until the sauce has thickened and the liquid is reduced, at least 20 minutes. Season with salt and pepper and stir the shrimp back in.