Peel and chop onion and carrots. Mince garlic, chop bell peppers, and cut chicken into cubes.
Add onion and carrots to the bottom of your slow cooker; add in garlic and peppers, then place chicken on top.
In a medium bowl, whisk together tomato paste, coconut milk, salt, pepper, curry powder, and garam masala.
Pour sauce over chicken and veggies, place lid on slow cooker, and cook on high for 3 -4 hours (or on low for 5-6 hours) until veggies are tender and chicken is no longer pink.
About 1/2 hour before serving, cook rice according to the package directions.
Serve curry over brown rice with mango slices on the side.