Grease a microwave-safe 9x12 inch baking dish, and set aside.
Heat a skillet over medium-high heat, and cook and stir the beef until crumbly, evenly browned, and no longer pink, about 10 minutes.
Drain and discard any excess grease.
Mix together the cooked ground beef, refried beans, oregano, and cumin in a bowl. Spoon the mixture into uncooked manicotti shells, and place the filled shells into the baking dish.
Combine the water and picante sauce in a bowl, and pour over the shells.
Cover the dish with microwave-safe plastic wrap, cut a few holes in the wrap with a knife to vent, and microwave on High power for 10 minutes. Carefully pull back the plastic wrap to avoid steam, and turn the shells over with tongs. Replace the plastic and microwave an additional 15 to 20 minutes on Medium power, until the shells are cooked and the liquid has been absorbed.
Pull off the plastic wrap, and spoon sour cream over the shells.
Sprinkle with Monterey Jack cheese and chopped green onions for garnish.
