Make the salsa verde: Combine the mustard greens, parsley, mint, tarragon, capers, anchovies, garlic and lemon zest in a large bowl. Stir in the olive oil and season with salt and pepper. Let sit at room temperature for at least 30 minutes before serving.
Make the scallops: Combine the paprika, brown sugar, cumin, ground fennel, coriander, mustard powder and 1 teaspoon salt in a small bowl. Season the scallops on both sides with salt and pepper, then sprinkle all over with the spice mixture. Rub the spices into the scallops.
Heat the canola oil in a large nonstick skillet over high heat until the oil begins to shimmer. Add the scallops to the pan in a single layer and cook until the bottoms are golden brown, about 2 minutes. Flip and cook until the other side is golden brown and the scallops are just cooked through, about 2 more minutes.
Serve 2 or 3 scallops per plate; top each scallop with a dollop of salsa verde, sprinkle with the Cotija cheese and top with a Fresno chile slice. Serve with chile paste and garnish with microgreens.