In a 5- to 6-quart pan, combine broth, peppercorns, coriander, allspice, and peel.
Bring to a boil on high heat; cover and simmer 20 to 30 minutes to blend flavors.
Sort and discard debris from lentils; rinse lentils.
Trim dark tops and root ends off leeks.
Split in half lengthwise, rinse well, and slice thin.
Peel squash and cut into 1/2-inch cubes.
Add lentils to broth; simmer, covered, for 15 minutes.
Add squash and leeks.
Cover and simmer until both are tender to bite, about 15 minutes.
Meanwhile, cut chard into 1/4-inch strips; rinse and drain.
Add chard to broth; simmer, uncovered, until wilted, about 5 minutes.
Add salt and pepper to taste.