Build a fire in your grill. When the coals are covered with gray ash, and the temperature is medium-hot, the coals are ready. If using a gas grill, turn the burners on high, cover and heat for 15 minutes, then lower the burners to medium-high.
Toast the peppercorns, coriander seeds, mustard seeds, and cardamom pods in a small dry skillet over medium heat, shaking frequently, until fragrant and slightly darkened, about 2 minutes. Remove from heat and allow to cool for a few minutes, then grind finely in either a mortar or spice mill.
Sprinkle shrimp with salt and pepper, then rub in the spice mixture, gently pressing it into the shrimp. Set aside.
Heat olive oil in a small skillet over medium heat. Stir in the ginger and cook, stirring, for 1 minute. Add the vinegar, orange juice, curry powder, and salt and pepper, then bring to a simmer. Reduce heat and cook for 3 minutes, stirring occasionally.
Arrange the peaches and spinach in a serving bowl and pour the hot dressing over both, wilting the spinach.
Arrange the shrimp on the grill and cook 3-4 minutes on each side, until just opaque throughout (slice open one of the shrimp to check).
Top the wilted spinach with the grilled shrimp, and serve.