In a container or zip-top bag, combine the garlic, herbs, oil, salt, pepper, and chile flakes. Add the chicken and marinate overnight or for at least 4 hours.
Preheat the oven to 400°F. Remove the chicken from the marinade, discard marinade, and arrange on a baking sheet. Roast until the chicken is cooked through, about 20 minutes. Let it rest, covered, before slicing.
For the relish, arrange the bell peppers on a baking sheet, toss with olive oil and salt and pepper. Roast for 15 minutes, until browned.
In a blender or food processor, blend ½ cup basil, mayonnaise, both vinegars, 1 garlic clove, sugar and salt until mostly smooth. Slowly stream in the oil with the motor running, until emulsified.
In a bowl, combine the roasted bell peppers, remaining basil, drained roasted red peppers, remaining garlic clove, pepperoncini, chile flakes and basil dressing. Toss well to coat and season to taste.
For the polenta, bring the water, milk, butter and salt to a boil in a large pot. Reduce heat to low and whisk in the polenta. Cook, stirring regularly, for 20 minutes.
Meanwhile, heat a skillet over medium heat with the sausage. Cook, breaking the sausage up with a wooden spoon, until the fat is rendered and the meat is cooked through. Fold the crumbled sausage, parmesan and cheddar into the polenta and cook for 10 more minutes. Season with salt and pepper.
To serve, divide the sausage polenta between plates. Top with a chicken breast, pepper relish and pine nuts.