Preheat oven to 350F.
Coat Roma tomatoes, half the onion, garlic cloves, and whole jalapeños with canola oil.
Spread on sheet pan and roast 30-40 minutes until charred, turning occasionally.
Let cool to room temperature, then remove stems, seeds, and membranes from jalapeños.
In blender, combine canned tomatoes, roasted Roma tomatoes, garlic, jalapeños, and cooked onion half and pulse until blended but not smooth.
Add salt, cilantro, and raw onion half and pulse to desired consistency.
Taste and add lime juice if desired.
Refrigerate at least 30 minutes before serving.