Our honey vinaigrette adds a splash of sweetness to the greens.
Preheat oven to 375 degrees. Make glaze: In a small bowl, whisk together 1 teaspoon mustard, 2 tablespoons vinegar, 2 tablespoons honey, garlic, rosemary, and 2 teaspoons oil.
Place pork tenderloins in a shallow baking dish; pour glaze over pork, turning to coat evenly. Sprinkle with 1/2 teaspoon salt; season with pepper.
Roast in oven, spooning glaze over pork occasionally, until thickest part of pork reaches 155 degrees on an instant-read thermometer, 30 to 35 minutes. Remove from oven; let rest until pork reaches 160 degrees, about 10 minutes.
Meanwhile, make vinaigrette: In a small bowl, combine remaining 2 tablespoons honey, 1 1/2 tablespoons vinegar, and 1 teaspoon mustard. Whisk until honey is dissolved. Slowly whisk in1 tablespoon oil until emulsified. Whisk in any accumulated cooking juices from baking dish, if desired.
Heat remaining 2 teaspoons oil in a 12-inch saute pan over medium-high heat. Add fennel, escarole, spinach, and a splash of water; cook until greens are slightly wilted, about 1 1/2 minutes.
Add vinaigrette and remaining 1/4 teaspoon salt to pan, stirring just to coat greens, about 30 seconds. Remove from heat; divide among four serving plates. Slice pork about 1/2 inch thick; arrange alongside greens. Serve immediately.