Sauté the Vegetables: Heat the vegetable oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook until softened, about 5 minutes.

Add More Vegetables: Add the diced carrot, bell pepper, and cook for another 3-4 minutes, stirring occasionally.

Simmer the Soup: Add the diced tomatoes, rinsed rice, potatoes, water, bay leaf, salt, and pepper to the pot. Bring to a boil, then reduce heat to low and simmer for 20-25 minutes, or until the potatoes and rice are tender.

Finish the Soup: Stir in the drained canned tuna and frozen green peas. Cook for an additional 5-10 minutes, or until the peas are heated through and the tuna is warmed.

Serve: Remove the bay leaf before serving. Garnish with chopped fresh parsley, if desired.