The question is a little vague but depending on whether you have access to the back of the frame there are several ways to attach.
Spacing is easy, by just using one batten to space, or offcuts if you have any.
Fixing from back of frame: Drill the frame at the relevant points for each batten and use a stainless steel screw with enough length to enter the timber no less than half way, the timber will probably require a predrill so as to not break the screw.
Fixing from the front of the frame: either use a stainless self tapping screw with a decorative head if the screws can be seen, or alternatively, counterbore and plug each hole over the screw for an invisible fixing. This can only be done providing you have enough timber that you can cut plugs from.
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