In a bowl, combine the lemon juice and Dijon mustard. Slowly pour in the ¼ cup extra virgin olive oil, whisking as it's added, until the dressing is smooth and emulsified. Season with salt and pepper.
Prepare Salad:
Combine the tatsoi or spinach with the radishes, mint, parsley and drizzle with a touch of extra virgin olive oil and a sprinkle of salt. Toss to combine.
Prepare the Buttery Sugar Snap Peas:
Melt the butter in a small skillet over medium heat. Once melted and frothy, and add the sugar snap peas and season with salt and pepper. Cook, stirring often, until tender-crisp and bright green, about 3-5 minutes. Turn off the heat.
To Serve:
Divide the salad between plates and pile the warm, buttery sugar snap peas on top. Arrange the torn mozzarella on top of each salad and serve with the dressing. Enjoy!