Preheat oven to 375F and move the rack to the middle position.
Sauté the onion in a cast iron skillet for 5-7 minutes.
Add the garlic to the skillet and cook for about 30 seconds or until fragrant.
Add the diced tomatoes, milk, Italian seasoning, thyme leaves, basil, and salt & pepper. Give it a good stir and let it heat through a bit.
Break the lasagna noodles into pieces so you can layer them in the skillet. There's no exact science to this and it's fine if they overlap a bit (all noodles should be mostly submerged in the sauce). Leave about an inch or so from the top so it doesn't bubble over as it cooks.
Place the skillet in the oven and bake for 40 minutes.
Take the lasagna out of the oven and top with the sliced cheese. Return the skillet to the oven for another 10 minutes or until the cheese is nice and melty. You can broil it for a few minutes at the end to make the cheese brown a bit if you wish (just watch it carefully).
Let the lasagna sit for about 5-10 minutes before serving.