For the pilaf, melt butter in saucepot over medium heat, add pasta and toast to deep golden and fragrant. Stir in rice and stock, bring to boil then reduce heat to low. Cover and cook to tender, 18 minutes.
Preheat oven to 375F.
Heat olive oil in a soup pot, 2 turns of the pan, over medium-high heat. Add carrots, celery, onions, garlic, bay, herb bundle, salt and pepper, and cook partially covered, 5-7 minutes to soften. Add stock and bring to a boil, reduce heat and simmer. Add lemon juice to broth just before serving.
Meanwhile, squeeze liquid from bread and crumble into moist crumbs as you add it to the beef in a mixing bowl. Beat egg and add to beef, season the meat with salt and pepper. Add onion, spinach, garlic, feta, lemon zest and a drizzle of EVOO. Roll meatballs about 1 1/2 inches and arrange on parchment-lined baking sheet. Roast meatballs until medium brown and lightly crispy, 25-30 minutes. Add to soup.
To serve, add rice to soup. If its too thick, dilute with water or stock. Serve in shallow bowls.