Trickle 1 tablespoon olive oil in the bottom of a roasting tin. Arrange chicken thighs in the tin. Mix the tomato puree and water, then spread over the chicken. Place garlic in the tin. Season chicken with salt and pepper. Arrange potatoes, tomatoes, onion, mushrooms and peppers over the chicken. Sprinkle with remaining tablespoon olive oil.
Bake 1 1/2 hours in the preheated oven, until vegetables are tender and chicken juices run clear. Periodically pour a little water into the tin if it starts to get dry.