Place the 4 boneless skinless chicken thighs in the slow cooker in a single layer.
In a mixing bowl, combine 1 cup crushed pineapple (with juice), 1/2 cup crushed tomatoes, 1/2 cup salsa, and 2 teaspoons soy sauce; stir until evenly mixed.
Pour the pineapple-salsa mixture over the chicken, coating each piece.
Cook on low for 6 hours or on high for 4 hours, until the chicken is cooked through and tender.
When done, remove the chicken and shred or serve whole as desired.
If you prefer a thicker sauce, mix 1 tablespoon cornstarch with 1/4 cup cold water, stir into the hot slow cooker sauce, and mix until thickened.
Serve the chicken and sauce over rice or quinoa.