Preheat oven to 375°. In large skillet, heat 1 tablespoon oil over medium heat. Add carrots and leeks; cook 2 minutes, stirring occasionally. Add garlic; cook 30 seconds, stirring occasionally. Add asparagus and mushrooms; cook 3 minutes or until mushrooms release their moisture, stirring occasionally. Stir in spinach; cook 2 minutes or until spinach is wilted. Remove from heat; stir in breadcrumbs, thyme and 1/8 teaspoon each salt and pepper. Makes about 1/2 cup.
To butterfly pork, cut pork lengthwise down center, leaving 1/2 inch uncut. Lay pork flat between plastic wrap on cutting board; pound to 1/2-inch thick with flat end of meat mallet. Remove plastic wrap; place vegetable mixture lengthwise down center of pork in 2-inch row. From long side, tightly roll pork around filling; secure with 3 wooden skewers.
Sprinkle pork with remaining 1/8 teaspoon each salt and pepper. In large skillet, heat remaining 1 tablespoon oil over medium-high heat; add pork and cook 4 minutes or until browned, turning once. Transfer pork to rimmed baking pan and roast 30 minutes or until internal temperature reaches 145°; let stand 10 minutes before slicing.