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Place milk, eggs, 1/3 cup flour, butter, sugar, and 1 teaspoon salt in a large bowl; combine well using a whisk or an immersion blender. Mixture should be the consistency of heavy cream. If mixture is too thin, add more flour. Add herbs and let stand 15 minutes.
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Place an 8-inch nonstick skillet or crepe pan over medium heat. Spray with nonstick cooking spray. Add a scant 1/4 cup batter and quickly swirl to coat the bottom of the pan. Cook until edges begin to dry, about 1 minute. Using your fingers or tongs, turn crepe, continue cooking about 15 seconds more, and then transfer to a plate. Repeat process with remaining batter, stacking each crepe on top of one another as you work.
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Preheat oven to 425 degrees. Place all the mushrooms in a large bowl. Drizzle with olive oil and season with salt and pepper; toss to combine. Spread mushrooms on a rimmed baking sheet in an even layer; transfer to oven and roast for 10 minutes. Remove from oven and let cool slightly.
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Place a crepe flat on work surface. Spread 1 tablespoon cheese evenly over three-quarters of the crepe. Top with about 2 tablespoons mushrooms. Starting with the covered portion, roll crepe toward the uncovered portion and place seam-side down on a baking sheet. Repeat process with 11 crepes and remaining cheese and mushrooms; reserve any remaining crepes for another use. Transfer filled crepes to oven until heated through, about 5 minutes.
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Meanwhile, place mustard greens and spinach in a large bowl. Add 1/4 cup marmalade and season with salt and pepper; toss to combine. Divide greens evenly between 6 plates and top each with 2 crepes. Spoon any remaining marmalade over crepes and serve immediately.