1. Cut tomato in half and squeeze out and discard seeds. Cut into 1/2 inch dice. Chop garlic. Drain tuna, pouring oil into 3-quart saucepan. Flake tuna with a fork and set aside. Heat oil from tuna with extra-virgin olive oil over medium heat. Add garlic and cook until fragrant, stirring frequently, about 1 minute.
2. Add rice and cook, stirring frequently, until it starts to look white, 2 to 3 min. Increase heat to high and gradually stir in clam juice and 1-1/4 cups water (see Note below). Bring to a simmer, stirring occasionally so rice doesn't stick to bottom of pot. Reduce heat to low and cover.
3. Cook until barely al dente, about 11 minutes. Stir in tomato and tuna and cook, uncovered, stirring frequently, until they heat through, 1 to 2 minutes. Add salt and pepper to taste. Makes 4 to 5 servings as a first course.
Note: White wine is often used in risottos as some of the liquid. If you like, substitute 1/2 cup dry white wine for 1/2 cup water.