Saute the onion in the oil and butter for a minute, until slightly golden. Add the garlic and rice, and stir to combine. Cook until rice starts to get pearly, being careful not to burn anything. Add the water and boullion, then the tomatoes & bell pepper. Bring to a boil, cover, and reduce to low. Once all the water has been absorbed, test for doneness, then add in frozen veggies. Recover pot and cook another minute or so, until veggies are warmed through. Fluff rice and incorporate veggies.