In large skillet, heat 1 tablespoon olive oil over medium-high heat. Add onion to skillet and cook until softened, about 6 minutes. Add garlic, pepper, and herbs, and cook 1 minute more. Transfer mixture to slow cooker. Add 1 tablespoon oil and half of lamb to skillet and cook, stirring occasionally, until meat is browned, about 8 minutes. Repeat with remaining 1 tablespoon oil and remaining lamb. Sprinkle flour over lamb in skillet and stir to coat. Transfer mixture to slow cooker. Add remaining ingredients, except zucchini. Cover and cook 5 hours on low.
Place zucchini in a microwave-safe bow, cover, and microwave 5 minutes. Stir zucchini into stew.