Preheat your oven to broil. Pop your tomatoes, garlic and chilies on a baking tray and coat them in olive oil, the salt, a healthy sprinkle of cumin seeds and crushed chili flakes, if you're using them. I've attached a picture here of how well I coat the veggies in the cumin and chili flakes, for reference, since I never measure it exactly.
Broil the veggies for about 10 minutes, or until you see some dark char on the peppers and garlic, and the tomatoes are soft.
Using a food processor or blender, puree the roasted veggies with the ground cumin and chili powder. When you have the consistency you like, add a splash of lime juice and the cilantro (I use about a cup of cilantro leaves, but you can add more or less as you like) and pulse to combine everything completely. Taste to see if it needs more salt, and add a pinch if necessary. Serve immediately or cool and serve chilled.
*If you like roasted onion in your salsa, just peel and quarter a small brown or yellow onion and pop it on the tray with the rest of your veggies. Nothing else with the recipe changes! I normally add onion when I make fresh salsa, but wasn't able to find any decent ones at the store during my last trip.