Heat the olive oil in a large heavy frying pan, add the rice and saute until the rice is nicely browned (watch it carefully.) Put the browned rice into the slow cooker.
Add the onions to the fry pan and cook until they start to brown, about 4-5 minutes. Then add the garlic, Greek seasoning, and dried oregano and cook a couple minutes more. Add the stock and scrape the pan to remove any browned bits; then add the onion/stock mixture to the slow cooker with the rice. Cook on high for 1 1/2 hours.
While the rice cooks finely chop the red bell peppers, and after 1 1/2 hours (or when the rice is fairly softened, but not completely done) add the bell peppers and cook 15 minutes more. While rice and peppers cook, crumble the Feta and slice the olives, then add the the slow cooker and cook another 15 minutes.
Chop the parsley and squeeze the lemon juice. Check to be sure the rice is as cooked as you'd like it, then stir in the chopped parsley and lemon juice and serve hot.