Set oven rack about 6 inches from the heat source and preheat the oven's broiler.
Line a baking sheet with aluminum foil; spread Hatch chile peppers on top.
Cook under the preheated broiler, turning once, until the skin of the peppers has blackened and blistered, 6 to 8 minutes. Transfer to a bowl and seal tightly with plastic wrap. Let cool, about 20 minutes. Peel and seed peppers; dice flesh.
Heat olive oil in a large pot over medium heat. Add onion and garlic; cook and stir until softened, about 5 minutes. Stir in diced chile peppers and tomatoes. Cook until heated through, about 5 minutes. Sprinkle flour into the pot.
Pour broth into the pot; add cumin, chili powder, and salt. Bring to a boil; reduce heat and simmer until flavors combine, at least 30 minutes.