I have made this without the jalapeno before and it still has plenty of heat from the Rotel tomatoes (and I even use mild). If you're trying this for the first time, you may want to start with no jalapeno and then taste it and see if you'd like more kick.
1 28-oz. can whole tomatoes
2 10-oz. cans Rotel tomatoes (diced tomatoes & green chiles - mild or original)
1/2 c. chopped onion
1 large clove garlic, minced
0-1 jalapeno, quartered and sliced thin (depending on spice preference)
1/2 c. cilantro, chopped
juice of 1/2 lime
salt, to taste
Throw all ingredients into a food processor and pulse until desired consistency is reached, about 10 pulses. You can do this in batches if it doesn't fit. (If I don't feel like chopping anything myself I start with the garlic and jalapeno in the processor - get it minced, then add the onion and cilantro - get that roughly chopped, and then just add the tomatoes and pulse a few times). Season with salt if desired.
Source: Adapted from Pioneer Woman