To make dressingHeat a small sauté pan over medium-high heat and pour in oil to about 1/8-inch deep.
When oil is hot, add pumpkin seeds and cook until puffed and beginning to brown (cover with a sieve to avoid popping seeds), about 1 minute.
Remove seeds from oil and drain on paper towels.
Using a mortar and pestle, grind 1 Tbsp pumpkin seeds with 2 Tbsp olive oil until seeds are broken down into small pieces.
(Alternatively, use a mini food processor.)
Combine with the lime juice in a small bowl and season with salt and pepper.
Slowly whisk in 4 Tbsp olive oil.
Place arugula in a serving bowl and arrange the mango and jicama on top.
Drizzle with dressing, sprinkle with remaining pumpkin seeds and some fresh black pepper.