In a 12 inch to 14 inch saute pan, heat together oil, onion and garlic over medium high heat until soft, about 8 to 10 minutes. Add eggplant and cook until just softened. Add tomatoes and lemon and season with salt and pepper and cook until they fall apart, about 4 to 5 minutes. Add calamari, season again, and cook until just opaque, about 2 minutes per side. Add basil and toss. Arrange on platter and serve.