For the roasted mushroom dippers: Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.

In a large bowl, toss the mushrooms with the olive oil and garlic salt. Add additional salt and pepper to taste.

Spread evenly on the prepared baking sheet, making sure there is space in between so the mushrooms don't steam. Bake, flipping halfway through, until golden brown and almost tender but still sturdy enough for dipping, about 25 minutes. (Keep the oven on.)

For the dip: Lightly grease a 2-quart baking dish with olive oil.

Heat a small skillet over medium-low heat and add the butter. Let melt, then add the panko and cook until golden brown, about 3 minutes. Season to taste and remove to a bowl to cool.

Heat a medium skillet with the tablespoon olive oil over medium-high heat. Add the sausage and cook, breaking it up into crumbles using a wooden spoon, until browned, 6 to 7 minutes.

Add the onion and cook until softened, 2 minutes or so. During the last minute of cooking, add the garlic and thyme and season with the ½ teaspoon salt. Remove from the heat and allow to cool to room temperature.

In a large bowl, add the cream cheese, mayonnaise, basil leaves, black pepper and ½ cup Parmesan. Stir until combined and smooth.

Add the cooled sausage mixture and spinach and fold until just combined. Spread evenly in the prepared baking dish.

Sprinkle with the cooled panko and remaining 2 tablespoons Parmesan. Bake until golden brown and bubbling, about 25 minutes. Garnish with the parsley. Rewarm the dippers, then serve together.