Bring 8 cups water and the bay leaves to a boil in a medium saucepan. Add lentils, and reduce heat. Cover with a round of parchment, and gently simmer until tender, 25 to 30 minutes. Drain lentils. Let cool completely, about 30 minutes. (Lentils may be made 1 day ahead and refrigerated.)
Heat oil in a large nonstick skillet over medium-high heat. Pat pork dry, and season with 1/2 teaspoon salt and some pepper. Cook until pork is browned and just cooked through, flipping once, about 6 minutes. Let rest on a platter, tented with foil, 5 minutes.
Meanwhile, finely grate 1 teaspoon zest from 1 orange. Cut peel and pith from remaining 2 oranges. Cut into quarters, and slice each quarter crosswise into 1/4-inch slices with a sharp knife, reserving juices. If necessary, squeeze zested orange to measure 1/4 cup juice total.
Toss together oranges, 1/4 cup juice, the lentils, basil, shallot, 2 teaspoons oil, 3/4 teaspoon salt, and 1/4 teaspoon pepper. Add any juices from resting pork.
Halve, pit, and peel avocado. Halve each half lengthwise, then cut into 1/3-inch slices crosswise, and fold into salad. Spoon salad over pork, garnish with basil, and drizzle with remaining oil.
When lentils are eaten with vitamin C-rich oranges, the iron they contain is more easily absorbed by the body.