Preheat oven to 450 degrees.
In a large, nonstick, pan over medium high heat, heat oil.
Add onion and garlic; saute until softened.
Add zest, lemon juice, salt, pepper and mustard seeds; cook one minute.
Stir in leafy greens; cover and cook until softened, about 7 minutes.
Remove from heat; stir in pecans.
Roll pastry to 12 x 9 inch retangle, spread leafy green mixture along centre. Along one length of pastry, make diagonal cuts almost to filling, 1 inch apart; repeat on other side. Alternating strips, fold over filling to form braid, brushing with egg to secure. Brush entire top of strudel with egg; sprinkle with salt. Transfer strudel to parchment lined baking sheet.
Bake until pastry is golden, about 20 minutes. Let cool slightly.
