Mix together the mashed sweet potatoes, eggs, salt, and pepper.
Add ~2 tbsp of the mixture to a waffle iron until crisped into "buns".
Form the ground beef into 4 patties and cook to desired temperature.
Blend the plain non-fat Greek yogurt with the 2 chipotles in adobo to make the chipotle yogurt sauce.
Assemble the burger: bun, lettuce, tomato, patty, cheese, chipotle sauce, top bun.
