Preheat oven to 300°F. Brown hamburger, and chopped onion until no longer pink; drain. Add soup (undiluted) and Ro*Tel to beef and onion mixture. Cook until boiling. Lower heat to a simmer, and simmer mixture until barely any liquid remains, stirring every so often.
In a 9x13 casserole, spread both cans refried beans evenly on bottom. Spread 1/2 beef mixture on top of beans. Add slices of Velveeta to just cover beef. Next add desired amount of jalapenos on top of Velveeta. Next add the rest of beef mixture, the rest of the Velveeta, and jalapenos to taste.
Bake until heated through and cheese is melted, about 20 minutes.