Rinse beans. In a large saucepan combine beans and 4 cups water. Bring to boiling. Reduce heat and simmer for 2 minutes. Remove from heat. Cover and let stand 1 hour. Drain and rinse beans.

Return beans to saucepan. Add 4 cups fresh water. Bring to boiling. Reduce heat and simmer, covered, about 1-1/2 hours or until beans are very tender. Drain beans, reserving cooking liquid.

For filling, in a large, heavy skillet cook onion and garlic in hot oil until tender. Remove from heat. Stir in drained beans and salt. Mash bean mixture, adding reserved cooking liquid (about 1/3 cup) to obtain desired consistency.

Meanwhile, wrap tortillas tightly in foil. Heat in a 350 degree F oven about 10 minutes or until heated through.

To assemble each burrito, spoon a scant 1/2 cup of the filling onto each tortilla just below center. Top with cheese and chopped tomato. Fold edge nearest filling up and over just until filling is covered. Fold in 2 adjacent sides just until they meet; roll up.

Arrange burritos, seam side down, on a baking sheet. Bake, covered, in a 350 degree F oven for 10 minutes. Uncover and bake for 5 minutes more.

If desired, serve burritos with chopped avocado, additional chopped tomato, and salsa. Makes 6 main-dish servings.

Prepare burritos as directed through Step 5, except do not add chopped tomato to filling. Wrap each burrito in foil and place in a freezer container. Freeze for up to 3 months. To reheat, place frozen burritos, loosely wrapped in foil, on a baking sheet and heat in a 350 degree F oven about 30 minutes. Open foil and bake for 10 to 15 minutes more or until heated through.