Place stock in a medium saucepan, and bring to a boil. Reduce heat; let simmer. Line a baking sheet with parchment; set aside.
Coat a large straight-sided saute pan with cooking spray; place over medium heat. Add onion, and saute until translucent, about 5 minutes. Add rice, and saute stirring, until the edges of the grains are translucent, about 1 minute. Add scallions, and cook, stirring, until bright green, about 1 minute.
Raise heat to medium high; add 1/2 cup simmering stock to rice, and cook, stirring constantly, until nearly all of the liquid has been absorbed. Continue adding liquid, 1/2 cup at a time, and cook, stirring constantly, allowing each addition to be absorbed before adding the next. With the last addition of stock, add peas; continue cooking until rice is creamy but grains are still firm in the centers, about 4 minutes. Remove from heat. Stir in dill and 1/4 teaspoon pepper.
Transfer risotto to a bowl, and let cool 30 minutes, stirring occasionally. Form into six patties, each 3 inches in diameter. Place patties on a prepared baking sheet, and cover with plastic wrap. Refrigerate 30 minutes.
Heat a nonstick skillet over medium-high heat. Add patties, and cook until browned, about 5 minutes. Turn patties, and cook until brown and hot, about 5 minutes more.
Combine vinegar, lemon juice, olive oil, salt, remaining 1/4 teaspoon pepper, and mint in a medium bowl; whisk to combine. Add greens; toss. Divide greens among six plates; top with rice patties. Garnish with dill; serve.