Quarter two onions and spread on the bottom of a slow-cooker.
Place chicken breasts on top of onions.
Season slow-cooker contents liberally with adobo seasoning, paprika and any other desired seasonings, squeeze half of a lime too if desired.
Let cook on low for 8 hours. Cooking on high for less time is possible as well, but a slower cook is preferable.
Dice the tomato, cilantro, any lettuce and the third onion for taco contents.
Shred chicken with forks once cooked. Optionally add a dash more seasoning for taste or appearance.
Add chicken, cheese and all the diced ingredients to tortillas.
Squeeze remainder of lime over finished product.