While the peas thaw, soak the cashews with the water in a glass container in the refrigerator.
Drain the cashews and transfer to a food processor. Add the olive oil, lemon juice, garlic, and salt and pulse into a thick paste, occasionally scraping down the sides of the food processor with a rubber spatula.
Add the peas and chopped fresh herbs to the cashews. Pulse and scrape into a fluffy, smooth paste. Taste the pea ricotta and add more lemon and salt if needed. Transfer to a container, tightly cover, and chill for at least 10 minutes for the flavours to blend.
When ready to serve, slice the tomatoes into thick slabs and arrange on a serving plate. Top each slice with a generous dollop of pea ricotta and garnish with a basil leaf. Drizzle each slice with olive oil, a little balsamic vinegar, and dust with a garnish of freshly ground pepper. Serve as is or with slices of crusty bread.