1. Bring stock to a simmer in a saucepan (do not boil). Keep warm over low heat.
2. Heat a large skillet over medium heat. Add 1 tablespoon oil to pan; swirl to coat. Add pasta; cook 5 minutes or until toasted, stirring frequently. Remove pasta from pan.
3. Add the remaining 1 tablespoon oil, shallots, garlic, and bacon to pan; cook 4 minutes or until browned. Remove bacon mixture from pan. Reduce heat to medium-low. Return pasta to pan. Add stock, 1 cup at a time, stirring constantly until each portion of stock is nearly absorbed before adding the next (about 35 minutes total), stirring frequently. Stir in bacon mixture, juice, rind, spinach, salt, and cheese. Garnish with oregano, if desired.