Wash tomatoes, cut off stem end, and slice in half lengthwise.
Place cut side down on rimmed baking sheet.
Chop onion into large chunks, add to baking sheet.
Cut stem off pepper, cut into chunks, add to baking sheet.
Drizzle with olive oil and bake at 400 degrees for 35 minutes, until tomatoes are wrinkled and starting to brown.
* Note: I had roasted garlic left over from another recipe that I used in the second step below. If you don't, just add fresh garlic cloves to the baking sheet and roast along with your tomatoes.
Add roasted tomatoes, pepper, and onion to food processor.
Add all other ingredients and blend until fairly smooth.
Adjust seasonings to taste, if desired, then use in your favorite enchiladas recipe.
Notes
Unlike many of the store bought varieties I looked at, my version is also gluten, corn, and soy free.