Place diced tomatoes in mircowave proof bowl. Cut jalapeno(s)in half, and onion in quarters. Add to bowl with cilantro, garlic, cumin and oregano. Microwave for 5 min. (I place a plate over the bowl while microwaving to avoid splattering). Once veggies have cooled a bit, place in food processor and puree, add a little water if you prefer thinner sauce.