Slow-Cooker Lasagna

INGREDIENTS

• 1 Tbs. olive oil
• 2 lb. Italian sausage, casings removed
• 2 jars (each 24 oz.) tomato sauce
• 2 cups water
• 1 lb. whole-milk ricotta cheese
• 2 Tbs. chopped fresh flat-leaf parsley
• Kosher salt and freshly ground pepper, to taste
• 18 ruffle-edged lasagna noodles (not no-boil noodles)
• 1 1/2 lb. mozzarella cheese, grated
• 2 oz. Parmigiano-Reggiano cheese, finely grated
• Thinly sliced fresh basil for garnish