Sauté the aromatics. Heat the olive oil and 1 tablespoon butter in a large skillet or deep pan over medium heat. Add the onion, bell pepper, and most of the green onions. Cook for 2–3 minutes, then add the garlic and cook about 30 seconds, just until fragrant.
Toast the rice. Add the rinsed rice and stir for about 2 minutes so the grains are coated in the seasoned oil and begin to lightly toast.
Season and simmer. Stir in the Old Bay, Cajun seasoning, turmeric or annatto, paprika, black pepper, crushed red pepper flakes if using, and a light pinch of salt. Add the broth, water, lemon zest, and lemon juice. Bring to a gentle boil, then reduce the heat to low, cover, and cook for about 15 minutes.
Add the seafood. When the rice is nearly tender, gently fold in the shrimp and crawfish tails. Cover and cook for 3–5 minutes, or until the shrimp are pink and opaque. Fold in the crab meat during the final 1–2 minutes so it warms through without breaking apart too much. If the rice looks dry before it is tender, add a small splash of broth or water.
Finish the dish. Remove from the heat. Gently fold in the tomatoes, if using, and the remaining green onions. For extra richness, stir in another tablespoon of butter. Taste and adjust the salt, seasoning, and fresh lemon juice.
Serve. Fluff gently and garnish with lemon slices or wedges and additional green onions. Serve hot.