If you haven't made the pesto in advance, make it now and set it aside.
Finely dice the onion, mince or press the garlic, and set both aside in a small bowl.
Chop the yellow squash into bite sized pieces, slice the cherry tomatoes in half, and set both aside.
Zest the lemon and set the zest aside.
Toss the breadcrumbs in a small bowl with the parmesan and a little bit of salt, pepper, and garlic powder and set them aside.
Melt the butter in a large (12") cast iron skillet over medium heat.
Add the sausage to the skillet and cook over medium heat for 6-8 minutes until just cooked through, stirring frequently and breaking up into bite-sized pieces.
Add the diced onion and cook over medium heat with the sausage for about 2 minutes, then add the minced garlic, Italian seasoning, and a couple pinches of salt and pepper and cook for an additional 2-4 minutes until everything is fragrant, the onions are translucent, and the garlic is slightly softened.
Add the gnocchi, spinach, broth, artichoke hearts, yellow squash, and ¾ of the sliced cherry tomatoes to the skillet and stir to combine everything. Then squeeze in the lemon juice and stir in all but ¼ cup of the pesto. Head over medium heat until the broth is just heated through, 1-2 minutes. Taste a bit of the mixture and season with salt, pepper, and optionally garlic powder or additional seasonings to taste.
Take the skillet off the heat and stir in the mozzarella, then top the skillet with an even layer of the breadcrumb mixture.
Place the skillet on a large baking sheet (to catch any potential drips) and place the sheet in the oven. Bake roughly 15-20 minutes until the sauce is bubbly and the breadcrumbs are golden brown and crispy.
Remove from the oven and drizzle the remaining pesto over the top of the breadcrumbs. Let the skillet cool 5-10 minutes before serving, then top with the lemon zest and optional fresh basil leaves.
You can play with this recipe a lot; try replacing the yellow squash with a different vegetable or using parsley or cilantro for the pesto instead of basil!