Prepare an ice-water bath; set aside. Bring a small saucepan of water to a boil. Blanch snap peas until bright green and crisp-tender, about 1 minute. Immediately transfer with a slotted spoon to ice-water bath to stop the cooking. Drain.
Transfer to a serving bowl. Add pea shoots, snap peas, lettuce, and radishes; set aside.
Prepare Warm Dressing
Heat a large nonstick skillet over medium heat until hot. Arrange pancetta in skillet in a single layer; cook, turning once, until crisp, about 12 minutes. Transfer with tongs to paper towels to drain.
Pour off all but 2 tablespoons fat (if skillet seems dry, add enough oil to total 2 tablespoons fat). Add onions; cook over medium-high heat, stirring often, until tender, about 4 minutes. Add wine; cook until most of liquid has evaporated, about 2 minutes. Add cream, and cayenne, if desired. Cook until liquid is reduced by half, about 4 minutes.
Pour warm cream dressing over greens; toss to coat. Season with salt and pepper, and top with reserved pancetta.
