Cook the pancetta in a large shallow skillet over medium heat until crispy, about 5 minutes. Add the shallots and cook until they start to soften, about 3 minutes. Add the garlic and stir until fragrant, about 30 seconds.
Add the frozen peas, and stir gently, cooking until the peas become hot and cooked through until tender, about 5 minutes. Remove pan from heat and stir in the butter until melted. Add salt and pepper to taste, and parsley if using. (Remember the pancetta is very salty, so taste before adding salt).