Set oven rack about 6 inches from the heat source and preheat the oven's broiler. Line a baking sheet with aluminum foil; add Hatch chile peppers.
Cook under the preheated broiler until the skin of the peppers has blackened and blistered, 5 to 8 minutes. Place blackened peppers into a bowl and tightly seal with plastic wrap. Allow peppers to steam as they cool, about 20 minutes. Remove and discard skins.
Blend roasted Hatch chile peppers, diced tomatoes, diced tomatoes with roasted garlic, onion, cilantro, and garlic powder in a food processor or blender until desired consistency is reached.