1. Prepare the grill to medium-high heat.
2. Cut baguette in 4 equal pieces and slice each piece open lengthwise; then with your fingers, remove about 1/2 the soft bread from the insides. then split each piece horizontally and pull out half the soft bread from each side, forming a boat.
3. Cut onion in half, around the equator, and dice half finely and slice 4 thin circles out of the other half.
4. In a large bowl, put the diced onion in with 1 tablespoon chutney and all the ground turkey; then mix together with your hands and form 4 burgers.
5. When grill is ready, put round onion slices on and cook 2 or 3 minutes on each side just until charred; remove.
6. Put burgers on at the same time and grill, flipping once, until meat is cooked through, about 5 to 6 minutes each side; remove.
7. Put bread pieces of grill if desired just to char the edges, about 1 or 2 minutes; remove.
8. To assemble - spread the remaining mango chutney on the open sides of baguette pieces, add the turkey burgers on 4 bottoms, put the grilled onion slices on top, then add lettuce and top with top bread piece. Makes 4 servings.