Heat oven to 350ºF. Grease 2-quart baking dish; set aside.
Melt 2 tablespoons of butter in a bowl in the microwave.
Place bread cubes into another bowl and pour melted butter over bread cubes; toss to coat.
Spread in an even layer on baking sheet.
Bake, turning cubes halfway through, for 20 minutes or until cubes are crisp and beginning to brown.
Melt 1 tablespoon butter in 10-inch skillet until sizzling; add green pepper and onion.
Cook for 5-7 minutes over medium-high heat, stirring occasionally, until crisply tender.
Place bread cubes, beef, green pepper and onion mixture and cheese into bowl; mix until well combined.
Transfer to prepared baking dish.
Whisk together all remaining ingredients in another bowl, then pour over ingredients in baking dish.
Cover with nonstick aluminum foil and bake for 40 minutes.
Remove foil and bake 10-15 minutes more or until knife inserted in center comes out clean.
Let stand 10 minutes before serving.