Thread the shiitake caps on 8 short wooden skewers. Arrange the skewers in a shallow, nonreactive pan.
To make the mojo, toast the cumin and peppercorns in a dry saucepan over medium-high heat until they’re quite aromatic. Grind them in a spice or coffee grinder and return them to the pan. Add the stock, sesame oil, honey, soy sauce, vinegar, ginger, and habanero. Bring to a boil and reduce to a simmer. After 5 minutes, remove the habanero; continue to simmer the sauce until it’s reduced to 1-1/2 cups, about another 10 minutes. Remove from the heat and strain the sauce through a fine sieve; let cool slightly. Pour the mojo over the shiitake skewers; let sit at room temperature for 30 minutes to 2 hours.
Light a grill or broiler. Remove the skewers from the mojo, letting any excess drip back into the pan. Transfer the mojo to a nonreactive saucepan and simmer until reduced to about 1/2 cup. Meanwhile, grill or broil the shiitakes until well-browned, 3 to 6 minutes.
Boil the somen noodles until just al dente (about 1 min. after the water comes back to a boil), drain well, and toss with the sesame oil. Mound the noodles in four shallow bowls, top with the grilled shiitake skewers, and drizzle with the reduced mojo.