Brown the beef and onion in a skillet over medium-high heat for 8 to 10 minutes until the beef reaches 160°F, then drain the fat.
Stir the garlic, chili powder and cumin into the beef for 30 seconds and cool the mixture completely.
Freeze the beef mixture with the lentils, tomatoes, pinto beans and salt in a labeled freezer bag for up to 3 months, then thaw it overnight in the refrigerator.
Transfer the contents to a 6-quart crockpot, stir in the broth, and cook covered on low for 5 to 6 hours until the lentils have nearly dissolved.
Stir in the vinegar and add 1/2 cup hot water only if the chili is thicker than oatmeal.