In a large pot heat oil over high heat. Crowd tomatoes, jalapeños, half of the white onion and garlic in a single layer in pan. Allow to cook on high without turning until vegetables are charred. Turn over and repeat on other side.
Once completely charred, about 3-5 minutes on each side, reduce heat to low and cover pot with a lid. Allow to simmer with lid on for 15 minutes. Once cooked remove from heat and allow to cool completely.
In a food processor add charred vegetables starting with only 1 jalapeño at a time along with crushed tomatoes. Add in cilantro, salt and other half of the white onion. Blend on low until desired texture is achieved. If not spicy enough, add more jalapeño one at a time.
Add in avocado and pulse until avocado is mixed in. Adjust salt as needed. Store for up to 1 week refrigerated in an airtight container.