Preheat the oven to 375 degrees F.
Place a large oven-safe braiser or large deep oven safe skillet over medium-high heat and add in the butter. Once butter melts, add in the mushrooms, shallots, thyme, salt and pepper. Stir occasionally until mushrooms and shallots are cooked down, release their liquid and begin to turn a slight golden brown, about 5 to 8 minutes. Stir in the garlic and cook for an additional 1 minute until the garlic is fragrant.
Deglaze the pan by stirring in the white wine and allowing it to simmer for 1 to 2 minutes over medium heat or until reduced by half, then stir in the orzo and toast in the pan for 1 minute to coat with flavor. Next, stir in chicken broth, heavy cream, tuna, salt, and LOTS of freshly ground black pepper. Bring mixture to a gentle simmer.
Bake: Place in the oven and bake, uncovered, for 15 to 20 minutes or until orzo is tender and cooked through.
While the orzo bakes, make the breadcrumb topping: In a medium bowl, use a fork to stir together the panko, parmesan cheese, thyme, salt and pepper. Next, stir in the melted butter until the mix is well coated.
Once orzo is done cooking, remove the pan from the oven and stir in the peas, cheddar cheese, and parmesan until well incorporated and cheese melts, 1 minute. Spread into an even layer then sprinkle the panko mixture on top.
Switch the oven to the broiler setting on high and broil, watching carefully until the panko is slightly golden brown in places, 2 to 3 minutes. Serve with extra salt and pepper to taste and some fresh chopped parsley on top! Lemon zest is also fabulous on this.