Comforting Beef and Yam Chili

1 lb. ground sirloin4 c. cubed unpeeled yams2 ½ c. beef stock2 c. chopped onion1 c. chopped red bell pepper¼ c. tomato paste2 T. chili powderKosher salt, red pepper2 t. ground cumin4 T. minced garlic2 (14.5-oz.) cans diced tomatoes, undrained1…