Heat the oven to 400°F and line a large baking sheet with parchment paper. Wearing gloves, halve the jalapenos lengthwise, scoop out the seeds and pale ribs, and arrange the halves cut side up on the sheet.
Stir the cream cheese, Greek yogurt, 3/4 cup of the cheddar, two-thirds of the scallions, garlic powder, smoked paprika and salt together in a bowl until smooth.
Spoon about 1 tablespoon of filling into each jalapeno half, mounding it slightly above the rim.
Toss the panko with the remaining 1/4 cup cheddar and scatter it over the filled peppers.
Bake 20-22 minutes, until the peppers are tender and the filling bubbles, then broil 2-3 minutes until the tops are golden; watch closely so the panko does not burn.
Cool 5 minutes on the sheet, scatter with the reserved scallions and serve warm.