Prick eggplant several times with the tip of a knife. Place it in a parchment-lined bamboo steamer set over boiling water, and steam until tender, about 10 minutes.
Heat olive oil and 1 tablespoon butter in a large skillet over medium-high heat. Add peas, and season with salt. Cook, covered, for 2 minutes. Transfer to a small bowl.
Bring a large pot of water to a boil; add salt and pasta, and cook until pasta is al dente, 4 to 6 minutes. Drain pasta. Meanwhile, in the same skillet you used for the peas, heat remaining tablespoon butter over medium-high heat. Add spring onions, parsley, sage, chives, garlic, cooked peas, salt, and 1 tablespoon water. Cook, covered, until onions are bright green, 3 to 5 minutes. Add arugula, and cook until wilted. Top cooked pasta with pea mixture. Garnish with 1 tablespoon chervil and 1 tablespoon grated Parmigiano-Reggiano cheese.
Remove eggplant from steamer, and cut lengthwise almost in half. Top each eggplant with 1/4 cup ricotta cheese; season with salt and pepper. Drizzle with olive oil, and garnish with 2 tablespoons grated Parmigiano-Reggiano cheese and remaining tablespoon chervil. Top each serving of pasta with a ricotta-stuffed eggplant, and serve immediately.