Toss cucumbers, strawberries, cardamom, a pinch of salt and 1 tsp sugar in a medium bowl and let sit for 10 minutes to allow sugar to dissolve and flavors to meld.
Mix crème fraiche, lemon juice, remaining sugar and a pinch of salt in a small bowl. Set aside.
Pulse pumpkin seeds, cayenne pepper and a pinch of salt in a food processor until finely ground.
Divide cucumbers and strawberries among plates and drizzle lemon cream over top. Sprinkle with ground pumpkin seeds.