Preheat the oven to 400 degrees F. Put the garlic cloves on a sheet of aluminum foil, drizzle with the olive oil and season with 1/4 teaspoon salt. Fold the foil over to create a sealed pouch and roast the garlic until the cloves are lightly browned and very tender, 30 to 45 minutes.
Meanwhile, bring the orange juice, sugar and sherry vinegar to a boil in a small nonreactive saucepan. Stir in the shallots and sliced chile pepper, return to a boil, then remove from the heat and allow to cool to room temperature.
Toast the fennel, coriander and mustard seeds and the peppercorns in a small sauté pan over medium heat for a few minutes, until lightly browned and very fragrant. Transfer the spices to a mortar and break up into smaller, coarsely ground pieces with a pestle.
Combine the roasted garlic and olives with the orange juice mixture, orange zest and spices in a medium bowl. Divide among jars. Marinate in the refrigerator at least overnight and up to 1 week.
To serve, transfer to an ovenproof serving dish and heat for about 10 minutes in a 300 degrees F oven.