Round one is making the nacho sauce. I started using the large cans of nacho cheese. I put it in a greased slow cooker. I mix in 2 C of milk, 1 jar of salsa, 1 of the cans of diced tomatoes, & the can of green chilis. Put on low & heat for 4 hrs. Watch to make sure it doesn't burn around the edges. I start stirring after 2 hrs. Serve as a dip or over chips. It also woks as a warm dip for veggies.
Round 2: put the finely diced veggies & the other can of diced tomatoes in a greased slow cooker; cover & cook 2 hrs. (This is how I sneak veggies into my meals so my kids can't pick them out. When I say finely diced, I mean FINELY diced. They just kinda disappear into the sauce.)
About an hour in, cook the ground beef (or chorizo), and drain. Add the cooked meat to the veggies in the cooker & continue cooking. After another hour, add in left-over nacho cheese sauce to heat through.
As the sauce is heating, prepare pasta shells according to package directions to al dente. Drain thoroughly & mix into nacho sauce. Let cook another 1/2 hr, until noodles have absorbed most of the sauce. Now you have Nacho Mac n Cheese.