Poke the sausages all over with a fork. Heat a large skillet over medium heat. Cook sausages, turning occasionally, until well browned on all sides. About half way through browning the sausages, add the garlic into skillet. Transfer the browned sausages and garlic to a large casserole dish, leaving the fat behind.
Preheat the oven to 400 degrees F.
Cook the onions, stirring often, until golden and just wilted. Remove to baking dish.Cook the mushrooms until they have absorbed the fat in the skillet and have begun to brown,
Add the mushrooms to the baking dish. (If there is not enough fat left to coat the bottom of the skillet, pour in enough olive oil to do so.) Add the peppers to the skillet and cook, tossing frequently, just until wilted.Add the peppers into the baking dish, toss all the ingredients together well and place in the oven.
Remove any fat from the skillet.Add the tomato paste. Add two tomato paste cans of chicken broth (about 1 1/2 cups) and stir to combine. Add the tomato paste mixture to the sausage and vegetable mixture, and season with salt,seasonings and black pepper to taste.
Bake uncovered, tossing occasionally, until the vegetables are tender but still firm and no trace of pink remains in the sausages, about 25 minutes.