Step 1: Preheat your oven broiler to high and line a baking sheet with aluminum foil.
Step 2: Arrange the serrano peppers, tomatoes (cut side down), onion wedges, and garlic cloves on the baking sheet.
Step 3: Place the tray under the broiler for 5-7 minutes, or until the skins of the peppers and tomatoes are charred and blistered.
Step 4: Remove the tray from the oven. Carefully peel the skin off the roasted garlic cloves and discard the skins.
Step 5: Place the roasted peppers, tomatoes, onion, and garlic into a food processor or blender.
Step 6: Add the lime juice, sea salt, and cumin to the mixture.
Step 7: Pulse the ingredients several times until you reach your desired consistency (chunky or smooth).
Step 8: Stir in the chopped cilantro by hand and taste for seasoning, adding more salt or lime if needed.
Step 9: Transfer to a serving bowl and let it sit for at least 15 minutes to allow the flavors to meld before serving.