Prepare. Prepare your ingredients as indicated. If you have not done so, wash, dry, and slice the tomatoes and peppers. Also, peel the garlic and chop the onion. Also, you will need a bowl and hot water.
Roast. In a dry skillet (no oil) over medium heat, carefully place the tomatoes with the cut side facing the skillet. Roast the tomato until charred (about five minutes) and then flip the tomato over and repeat with the other side. Set your roasted aside.
Chilis. In the same skillet, toast the dried chiles for about 30 seconds per side until fragrant, then place them into your bowl and cover with hot water. Let the chilis soak for five minutes.
Blend. Next, place your ingredients into a blender (roasted tomatoes, rehydrated chiles, garlic, onion, salt, cumin, and ½ cup of water). Blend the ingredients until smooth.
Heat. Heat the vegetable oil in your skillet over medium heat for one minute. Pour the salsa from the blender into the skillet and simmer for five minutes, stirring occasionally, until slightly thickened. Let the salsa cool to room temperature before serving.