Cut chicken breasts into bite-sized pieces. Dice the onion and bell peppers. Mince the garlic.

Heat olive oil in a large skillet or Dutch oven over medium-high heat. Add chicken and cook until browned on all sides. Remove chicken and set aside.

Add onion and bell peppers to the skillet and sauté until softened, about 5-7 minutes. Add minced garlic and cook for another minute until fragrant.

Stir in the tomato paste and cook for 1 minute. Return the chicken to the skillet. Add diced tomatoes, chicken broth, oregano, smoked paprika, salt, and black pepper. Bring to a simmer, then reduce heat, cover, and cook for 15-20 minutes, or until chicken is cooked through and sauce has slightly thickened.

While the chicken is simmering, peel and boil the potatoes until fork-tender. Drain well. Mash the potatoes with butter and milk until smooth. Season with salt and pepper.

Preheat oven to 191 °C (190 °C). Pour the chicken mixture into a baking dish. Spread the mashed potatoes evenly over the chicken mixture.

Sprinkle the shredded cheddar cheese over the mashed potatoes. Bake for 15-20 minutes, or until the cheese is melted and bubbly and the topping is lightly golden.

Let rest for a few minutes before serving.