Sautee 3/4 of the onions in olive oil for about 5 minutes. Add the ground beef, and cook another 5-7 minutes, draining off any fat after cooked. Add the cumin, salt and pepper, or season to taste.
Add a can of drained black beans.
To make the salsa, mix the diced beets, strawberries, chives, cilantro, honey and lime juice together. Hot sauce optional! Lightly salt; set aside.
To make the guacamole, mix the mashed avocado, sour cream, 1/4 cup onions, and lime. Season to taste.
Layer on top of the prepared tostada shell a thick layer of guacamole. Spoon the beef and bean mixture on top, ending with the salsa.