Cook first 8 ingredients in a large nonstick skillet over medium-high heat, stirring often, 10 minutes or until vegetables are tender. Drain on paper towels; cool.
Stir together ground beef and next 4 ingredients in a large bowl; stir in sausage mixture. Shape meat mixture into an 11 1/2- by 4-inch loaf; place in a lightly greased aluminum foil-lined 15- by 10-inch jellyroll pan.
Bake at 375 degrees for 50 minutes or until meat mixture is no longer pink in center; drain meat loaf, and let stand 10 minutes. Serve with Tomato Gravy.
To make Tomato Gravy, melt butter and whisk in flour and cook, whisking constantly for 1 minute. Gradually whisk in broth and tomato sauce. Reduce heat and simmer until thickened. Whisk in salt and pepper.