You can, and should ,modify this recipe by what your tastes call for.
Extra spicy? Add more peppers.
Extremely spicy? Add even more peppers (Habeneros perhaps?)
More sweet? Roast the tomatoes longer and remove the lime juice?
Take this base and make it as is (it's my favorite rendition at least) and do whatever you want to it to make it your own custom Salsa Roja Asada.
Step 1: Ingredients
7 Roma Tomatoes
3 Serrano Chili Peppers
1 White Onion
1-2 Limes (depending on taste)
4-5 Cloves of garlic
HEAVY handful of Cilantro
2tsp of salt
5-6 grinds of fresh black pepper
drizzle of olive oil
Step 2: Chop.
For the serrano peppers, use gloves to halve and remove most of the seeds with the edge of the knife. Be sure to protect your hands when handling serranos. If you wear contacts you'll be sorry you didn't.
Step 3: Roast.
Step 4: Dice. (or puree!)
Alternatively, you can chop for a much thicker, chunkier consistency; although this salsa is most often served pureed.
Note the hardcore in-food processor camera.