Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius).

In a small bowl, combine the sour cream and ricotta cheese until smooth. Set aside.

Spread 1/4 cup butter over the bottom of a 9×13-inch (23×33-centimeter) baking dish.

Arrange four oven-ready lasagna noodles in an even layer in the dish. Spread Alfredo sauce over the noodles, followed by dollops of the ricotta mixture. Arrange a layer of zucchini over the cheese mixture and sprinkle with one cup of the shredded mozzarella and cheddar blend.

Add another layer of noodles. Spread with Alfredo sauce and ricotta mixture, then arrange the yellow squash in an even layer. Sprinkle with one cup of the shredded cheese blend.

Add a third layer of noodles. Spread with Alfredo sauce and ricotta mixture, then arrange another layer of zucchini over the top. Sprinkle with one cup of the shredded cheese blend.

Finish with a final layer of noodles. Spread the remaining Alfredo sauce over the noodles and add dollops of the remaining ricotta mixture. Sprinkle with shredded mozzarella cheese.

Arrange remaining zucchini and yellow squash, together with sliced portobello mushrooms, decoratively over the cheese layer.

In a small saucepan, melt remaining 1/4 cup butter. Stir in the chopped sun-dried tomatoes, salt, pepper, and garlic powder. Drizzle the mixture evenly over the vegetables.

Lightly spray a sheet of foil with cooking spray and cover the baking dish, sprayed side down. Bake for one hour and 15 minutes.

Remove foil and continue baking for 10 minutes, or until the vegetables are tender and the top is lightly golden.

Allow lasagna to rest for 10–15 minutes before slicing and serving.