Heat the oil in a medium saucepan and sauté the onion, garlic and jalapeños until soft. Add the undrained tomatoes and cook over medium heat for about 5 minutes to reduce the liquid.
When the tomatoes begin to appear dry, reduce the heat to medium-low and start adding the cheese, 1 handful at a time, stirring over medium-low heat until the cheese melts; wait for each handful to melt before adding more cheese.
Serve in a chafing dish or fondue pot to keep the queso warm. Serve with corn chips, tortilla chips, or cut-up vegetables.
Servings: 2 1/2 cups; 10 (1/4 cup)