Cut away peel and pith from orange. Quarter orange, then slice crosswise into 1/4-inch-thick pieces. Heat 2 tablespoons oil in 10-inch skillet over medium heat until shimmering. Add jalapeños and shallots and cook until slightly softened, about 5 minutes. Stir in garlic and cook until fragrant, about 30 seconds. Transfer jalapeño-shallot mixture to medium bowl; stir in remaining 2 tablespoons oil, orange, jícama, pepitas, cilantro, lime juice, sugar, salt, and pepper. Serve warm or at room temperature.

Makes About 2 cups