1. Put a large pot of lightly salted water on to boil over high heat. Add spaghetti and cook until tender but still firm.
2. Meanwhile, heat large nonstick skillet over medium-high heat. For easy chopping, use kitchen shears to cut bacon slices crosswise into thin pieces. Add bacon to skillet and cook, stirring, 5 minutes. Remove bacon fat and discard.
3. Stir marinara sauce into bacon; heat 2 minutes. Stir in peas and mozzarella; heat another minute or two, just until cheese begins to melt and peas are warmed. Remove from heat and cover. Drain pasta and toss with sauce.