• Preheat oven to 375 degrees.
  

Prepare Rice:

• Combine rice, ½ teaspoon salt, and 1 ¾ cups water in a large heavy bottom pot.
  
• Bring to a boil, then reduce heat to low and cover. Cook rice for about 12 minutes or until tender (do not overcook). Set rice aside and keep covered.
  

Prepare Veggies:

• While rice is cooking, heat 2 teaspoons olive oil in a large skillet with a lid over medium-high heat.
  
• Add onions to pan. Season with salt and pepper, then cook for a few minutes or until they start to turn translucent, stirring frequently.
  
• Mix mushrooms into onions and cook, stirring often, until any liquid they've released has evaporated, and they are starting to brown. Season with salt and pepper.
  
• Reduce heat to medium, then spread broccoli florets over onions and mushrooms. Add 2 tablespoons water to pan and cover immediately.
  
• Steam broccoli for 4 to 5 minutes or until crisp-tender. (There should be no water left in the pan when the broccoli is done.) Sprinkle broccoli lightly with salt, then transfer broccoli mixture to a large bowl.
  

Prepare Sauce:

• Wipe out skillet used to saute veggies and return to stove over medium heat.
  
• Melt butter in skillet, then add garlic and saute for about 30 seconds or until fragrant, stirring constantly.
  
• Whisk flour into butter and cook, stirring constantly, for a couple minutes or until lightly golden.
  
• Slowly pour milk into butter mixture, whisking constantly until smooth. Bring to boil, then immediately reduce heat and cook, stirring often, until mixture thickens (it should coat the back of a spoon).
  
• Remove sauce from heat, then whisk in 1 ½ cups cheddar cheese (in two batches) until smooth. Season generously with salt and pepper to taste.
  

Assemble Casserole:

• Spray a 9 x 13-inch baking pan or large casserole dish with nonstick cooking spray. Set aside.
  
• Pour cheese sauce over veggies and mix well.
  
• Fluff rice with a fork, then fold into veggies (be careful not to over mix or the rice will get mushy).
  
• Transfer veggie-rice mixture to baking dish, then sprinkle with ½ cup cheddar cheese.
  
• Mix together panko, olive oil, ½ teaspoon salt, and ⅛ teaspoon pepper. Sprinkle over casserole.
  
• Transfer casserole to oven and bake until hot, bubbly, and browned on top (about 25 minutes).
  
• Serve casserole hot. Enjoy!