To prepare almond pesto, combine first 5 ingredients in a food processor; process until blended and a paste forms. Cover and refrigerate.
Preheat oven to 350°.
To prepare spice rub, combine marjoram, paprika, 1 teaspoon black pepper, and 1/4 teaspoon salt. Trim fat from beef; rub surface of beef with spice rub.
Heat oil in a large Dutch oven over medium-high heat. Add beef; cook 5 minutes, browning on all sides. Remove from pan. Stir in sherry, scraping pan to loosen browned bits. Return beef to pan. Add onion, tomatoes, 1 cup beef broth, and bell peppers. Cover tightly with lid. Bake at 350° for 3 hours or until meat shreds easily with a fork. Remove beef from pan. Cut beef into 2-inch pieces. Add almond pesto to pan, stirring until blended. Place pan over medium heat; cook 10 minutes. Stir in 1/4 teaspoon salt and 1/4 teaspoon black pepper. Serve beef and sauce mixture over rice.