Cook the ground beef in a large skillet over medium-high heat, breaking it up as it cooks. You are looking for no pink remaining and some real browning on the pieces; that color is flavor. Do not skip this step and add raw beef to the slow cooker. It will cook through, but the flavor will be flat and the texture will be soft in a way that doesn't work here.
1 Pound Ground Beef
Add the garlic. Stir in the minced garlic and cook for 1 to 2 minutes. Watch it. Garlic burns fast, and burnt garlic is bitter all the way through the finished dish. The moment it smells fragrant, move on.
1 Teaspoon garlic
Add the pasta sauce and Italian seasoning directly to the skillet. Stir to combine and let it simmer for 2 minutes. Taste it now and season with salt and pepper. Those 2 minutes let the flavors marry together before they go into the slow cooker.
2 24 ounce jars pasta sauce, 2 Teaspoons Italian Seasoning, Salt and pepper
Spread one-third of the meat sauce in the bottom of the slow cooker insert. This base layer prevents the ravioli from sticking and scorching on the bottom. Don't skip it.
Arrange the frozen ravioli in a single, even layer over the sauce. Overlap is fine; stacking too deep in one spot means uneven cooking. Spread them out as flat as you can.
25 ounces frozen raviolis
Top the ravioli with another third of the sauce. Every exposed ravioli edge should have sauce coverage. Dry corners turn chewy and tough.
Add the remaining frozen ravioli in the same flat, even pattern as before.
Pour the last of the meat sauce over the top and spread it to cover every visible ravioli edge. If a corner is sticking out, tuck it under or spoon sauce over it.
Cover and cook on low for 3 to 4 hours. Start checking at the 3-hour mark. The ravioli should be tender and cooked through; the sauce should be bubbling at the edges. Every slow cooker runs a little differently — mine is consistently done at 3 hours. Past 4 hours, the ravioli goes soft and the layers lose their definition.
Add the mozzarella. In the last hour of cooking, scatter the shredded mozzarella over the top. The cheese will melt into a clean, even layer without going oily or separating. Adding it at the beginning gives you greasy, overcooked cheese; the last hour is the window.
2 Cups mozzarella cheese