Preheat oven to 350 degrees F.
Heat the oil in a large oven-safe sauce pot or skillet that has a lid over medium heat (see notes if you don’t have an oven-safe pan). Add the onions, celery and garlic with a pinch of salt and pepper. Cook for 3-4 minutes until fragrant and soft.
Add sausage, serrano pepper and bell peppers and cook for an additional 6-7 minutes stirring frequently.
Add spices, rice, salt and pepper and cook until rice is lightly toasted, stirring often for about 2 minutes. For more heat, add up to 1/2 tsp cayenne pepper or red chili flakes with the other spices.
Add Liquid & Bay Leaf: Add crushed tomato, vegetable stock and bay leaf. Bring to a rapid boil then remove from heat and cover. Carefully place the entire pan in the oven, covered, and cook until the rice is tender, approximately 20-25 minutes. Remove from oven, remove lid and let sit for 5 minutes.
Serve right away, garnished with parsley and hot sauce, if desired, and enjoy!