user: Question: On what date(s) was the winning team Prema Powerteam?
Columns: ['Round', 'Circuit', 'Date', 'Pole Position', 'Fastest Lap', 'Winning Driver', 'Winning Team']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Autodromo Nazionale Monza', '30 March', 'Eric Salignon', 'José María López', 'Augusto Farfus', 'RC Motorsport']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Winning Team" = 'Prema Powerteam';