Place chicken in the bottom of a slow cooker. Top with onion, jalapeno, garlic, and seasonings.
1 pound (453g) boneless skinless chicken breast, 1 pound (453g) boneless skinless chicken thighs, 1 (8oz) (226g) can tomato sauce, 1 small onion, diced, 1 jalapeno; stemmed, seeded, and minced, 6 cloves garlic, minced, 2 tablespoons chili powder, 2 teaspoons cumin, 1 teaspoon dried oregano, 1 teaspoon salt