Melt 1 Tbsp. butter in large ovenproof skillet on medium-high heat.
Add vegetables; cook and stir 5 to 7 min. or until crisp-tender.
Remove from heat.
Stir in croutons, water and half the cheese.
Use sharp knife to partially cut steak horizontally in half, starting at thickest side of steak and being careful not to cut through to opposite side of steak. Open steak.
Spread vegetable mixture onto one cut side of steak; roll up, starting at one long side. Tie closed with kitchen string.
Melt remaining butter in same skillet.
Add meat; cook 7 to 8 min. or until evenly browned, turning occasionally.
Place skillet in oven.
Bake 35 min. or until steak is medium doneness (160F).
Remove from oven. Top steak with remaining cheese; let stand 10 min.