Preheat oven to 375°F.

To make the filling, melt butter in a large cast iron skillet over medium-high heat. Add onion and garlic and cook until just beginning to soften, about 5 minutes. Stir in mushrooms and cook 5 minutes. Stir in artichokes and spinach; season with salt, pepper and red pepper flakes. Cook until the spinach has wilted. Stir in chicken stock and chicken; simmer until liquid has reduced slightly, about 10 minutes. Transfer to a large bowl, and set aside.

To make the sauce, return skillet to stove and add butter. Once melted, stir in garlic, cooking until lightly browned. Stir in heavy cream and bring to a simmer. Add pepper and parmesan cheese; cover and cook over low heat until sauce has thickened and slightly reduced, about 5 minutes. Stir in mozzarella and cook until cheese has melted and the sauce is smooth, about 5 minutes longer. Pour sauce over filling in bowl and stir to coat.

To assemble the lasagna, spoon 1/4 of the filling into the bottom of skillet. Place 2 lasagna sheets on top and fill any gaps around the sides with broken pieces of pasta. Top with 1/4 of the filling; sprinkle with mozzarella cheese. Repeat the layering process two more times; finishing with remaining mozzarella cheese.

Cover with foil and bake 25 minutes. Remove foil and bake 10 minutes more, or until top is golden brown and bubbly. Remove from oven and let cool slightly before sprinkling with feta and fresh oregano. Cut and serve. Enjoy!