The least code way would be to make a png file with one cell of that grid and then set it to tile in a TextureRect (with import Filter unchecked)
Or with a bunch of code
tool
extends Control
export var bg = Color(1,1,1)
export var fg = Color(0.6,0.5,0.5)
export var rows = 3
export var columns = 3
func _draw():
var w = rect_size.x
var h = rect_size.y
var cw = w/columns #cell width
var ch = h/rows #cell height
draw_rect( Rect2(Vector2.ZERO,rect_size), bg)
for row in range(1,rows, 2):
var y = ch*row+(ch*0.5)
draw_line( Vector2(0,y), Vector2(w,y), fg, ch )
for column in range(1,columns, 2):
var x = cw*column+(cw*0.5)
draw_line( Vector2(x,0), Vector2(x,h), fg, cw )