Add the olive oil to a large Dutch oven over medium-high heat. Once hot, add the onions and peppers and saute until soft, about 4 minutes. Add the garlic and saute until just fragrant. Stir in the beef and sausage, breaking it up with the back of a wooden spoon, and cook until browned. Drain the beef mixture through a colander placed over a large bowl. Add the meat back to the Dutch oven and stir in the chili powder, cumin and oregano. Cook for about 2 minutes. Stir in the tomato paste into the beef; this will "toast" it and give the chili more flavor. Add the beer and stir up any browned bits on the bottom of the pan. Bring to a simmer, and then add the diced tomatoes and beans. Simmer on medium-low for 2 hours, stirring on occasion to keep the bottom from sticking.

Top with shredded cheese, sour cream and chopped green onions before serving.