Place chicken breasts in the bottom of the slow cooker and pour tomatoes over chicken. Mix together the Alfredo sauce, garlic cloves, pepper, salt and basil then pour over the chicken.
Cook on low 5 to 6 hours or high for 3 to 4 hours. When cooking is complete, remove chicken and shred it. Return chicken to slow cooker and add tortellini. Cook on low for another 15 minutes then mix in spinach. Cook until spinach has wilted, about 1-2 minutes. Serve!