In a large stockpot over high heat, bring 4 quarts of salted water to a boil. Add 2 tablespoons olive oil. In a large saute pan over medium high heat, add remaining 2 tablespoons olive oil and sausage. Cook until sausage is browned, about 6 minutes. Add zucchini, squash, onions, red pepper and 1/4 cup chopped basil and cook for 4 to 5 minutes, or until the squash has begun to caramelize. Season with salt and pepper. Add pasta to the boiling water and cook until just al dente, about 1 minute. Drain reserving 1/2 cup pasta water.
Pour cooked pasta and 1/2 cup pasta water into the sausage sauce. Garnish with basil sprigs and Essence.