Anyone know how i can restrict my staregy to only open 1 trade per day ?

If you BarPeriod is 1440, then only 1 trade can be generated per day, usually.

If you have a shorter BarPeriod, perhaps you can check the various trade stats for trade or no trade in the current bar.

http://zorro-project.com/manual/en/winloss.htm

Or you can use a global variable with the date of the last trade, if today=lasttradedate, then don't enter another trade.

thanks