Heat oil in a large non-stick saucepan over medium heat. Add onion. Cook until golden, about 10 minutes. Add pumpkin, stock, sage, salt and pepper. Cook, covered, just until pumpkin is tender, about 20 minutes.
Meanwhile, cook tortellini in a large saucepan of lightly salted water until al dente, following packet instructions. Drain. Toss with ricotta in a large bowl.
Add pumpkin, romano and parsley to tortellini mixture. Toss gently to combine.
Romano is an Italian hard cheese suitable for grating. Made from sheep's milk, its flavour is sharper than that of parmesan, a hard grating cheese made from cow's milk. The two cheeses are interchangeable, or you can combine them. Asiago is another Italian hard cheese for grating. Made from cow's milk, its flavour is somewhere between that of parmesan and romano.