Preheat the oven to 400 degrees and grease a 9x13 baking dish.
Melt the vegan butter in a large skillet over medium heat. Add the onion, garlic and a pinch of salt & pepper and cook down for 2-3 minutes. Add the broth and bring it to a boil. Pour in the squash, cover and lower the heat. Simmer for 20 minutes.
Meanwhile, bring a large pot of water to a boil. Add the pasta and cook until al dente - don't overcook it! Drain and set aside.
Remove the lid from the skillet and add the Boursin, mozzarella, mayo and yogurt. Gently mix until the cheeses are melted and everything is combined. Stir in the green chiles, garlic powder, onion powder and mustard powder. Taste and adjust the seasonings as needed. Pour in the cooked pasta and mix until combined.
Mix together the bread crumb ingredients. Transfer the pasta & sauce to the prepared baking dish. Sprinkle the bread crumbs over the pasta and cover with foil. Place in the oven for 20 minutes. Remove the foil and cook for another 10 minutes - turn the oven to broil for the last couple minutes for a crispier top.
Remove from the oven and allow to set for 5-10 minutes. Spoon onto plates & serve!
Video
Notes
If you can't find the dairy-free Boursin my next choice would be Kite Hill chive cream cheese.
The chiles are optional but add a great flavor. If you get a mild version they won't add any spice.
Be sure not to overcook the pasta since it will finish cooking in the oven.
I bought my squash pre-cut, but you can also peel and de-seed a whole one. Be sure to cut the pieces in uniform squares so they cook evenly.
To freeze: Prepare the casserole up until the baking step. Allow it to cool completely before covering and placing in the freezer. To reheat, preheat the oven to 350 degrees and bake for 60-ish minutes. Remove the cover and turn the oven to broil for a few minutes to get the top nice and crusty.