1. Combine first 4 ingredients in a small bowl. Rub mixture evenly over ribs.
2. Brown ribs, in batches, in hot oil in a large nonstick skillet over medium-high heat 5 minutes or until browned. Place ribs in a 6-qt. slow cooker; sprinkle with any remaining brown sugar mixture, and top with onion slices.
3. Stir together 1 1/2 cups beef broth and 3 Tbsp. lime juice, and pour over ribs in slow cooker.
4. Cook, covered, on HIGH 4 to 5 hours or on LOW 8 to 10 hours. Remove ribs from slow cooker, and place on a heated plate. Cover with aluminum foil.
5. Skim fat from broth mixture in slow cooker. Pour mixture through a fine wire-mesh strainer into a small saucepan. Bring to a boil over medium-high heat.
6. Stir together cornstarch and cold water. Stir into boiling broth mixture; reduce heat, and simmer, stirring constantly, until mixture is thickened (about 2 minutes). Add peach marmalade, and stir until marmalade melts and is blended. Keep warm.
7. Bring remaining 1 3/4 cups beef broth to a boil in a medium saucepan over high heat. Stir in rice. Cover, reduce heat to low, and simmer 20 minutes or until broth is absorbed and rice is tender. Remove from heat, and stir in baby spinach.
8. Spoon rice mixture onto a serving platter. Arrange ribs around rice mixture, and pour peach gravy evenly over top of ribs. Garnish, if desired.