Place tomatoes, onion, jalapeños, and garlic (skin on) on a cast-iron pan or lined baking sheet. Dry roast on medium-high heat, rotating until all sides are blackened and charred. The onion may begin to come apart as it roasts, which is totally fine. If using a broiler, broil for 7 minutes, rotate with tongs, then add garlic on the second round and broil for another 7 minutes. Set aside to cool.
Once cooled, remove the skin from the garlic and the stem from the jalapeno. Transfer everything to a blender. Add cilantro and lime juice. Pulse until you reach your desired consistency.
In a skillet, heat olive oil over medium heat. Once oil is hot, pour in the blended salsa and let it cook for about 3 minutes, stirring occasionally.
Add a splash of water to the empty blender, swirl to pick up any remaining bits, and pour into the skillet. Stir to combine, season with salt to taste, and serve.